Recently, CMP (Chemical Mechanical Polishing) is widely used in the manufacture of semiconductor devices in order to planarize an insulating film, metal film, or polysilicon film formed to fill trenches formed in a substrate. CMP is a method by which a polishing agent (slurry) containing abrasive grains and a liquid chemical is supplied onto polishing cloth, and the polishing cloth is brought into contact with an object to be processed, thereby planarizing a surface to be processed by combining a chemical action of the liquid chemical and a mechanical action of the abrasive grains. However, this method has the problem that polishing damage occurs on the surface to be processed because mechanical damage by the abrasive grains is unavoidable.